Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry. For example, the processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information indicates that a prediction of the current block is at least partially based on an inter prediction. Then, the processing circuitry reconstructs at least a sample of the current block as a combination of a result from the inter prediction and neighboring samples of the block that are selected based on a position of the sample.

INCORPORATION BY REFERENCE

This present application is a Continuation of U.S. patent application Ser. No. 16/777,339 filed Jan. 30, 2020, and claims the benefit of priority to U.S. Provisional Application No. 62/800,400, “ENHANCEMENT FOR POSITION DEPENDENT PREDICTION COMBINATION” filed on Feb. 1, 2019, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to video coding.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a series of pictures, each picture having a spatial dimension of, for example, 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable picture rate (informally also known as frame rate), of, for example 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080 luminance sample resolution at 60 Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of such video requires more than 600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction of redundancy in the input video signal, through compression. Compression can help reduce the aforementioned bandwidth or storage space requirements, in some cases by two orders of magnitude or more. Both lossless and lossy compression, as well as a combination thereof can be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between original and reconstructed signals is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely employed. The amount of distortion tolerated depends on the application; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television distribution applications. The compression ratio achievable can reflect that: higher allowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broad categories, including, for example, motion compensation, transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding. In intra coding, sample values are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, the picture is spatially subdivided into blocks of samples. When all blocks of samples are coded in intra mode, that picture can be an intra picture. Intra pictures and their derivations such as independent decoder refresh pictures, can be used to reset the decoder state and can, therefore, be used as the first picture in a coded video bitstream and a video session, or as a still image. The samples of an intra block can be exposed to a transform, and the transform coefficients can be quantized before entropy coding. Intra prediction can be a technique that minimizes sample values in the pre-transform domain. In some cases, the smaller the DC value after a transform is, and the smaller the AC coefficients are, the fewer the bits that are required at a given quantization step size to represent the block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2 generation coding technologies, does not use intra prediction. However, some newer video compression technologies include techniques that attempt, from, for example, surrounding sample data and/or metadata obtained during the encoding/decoding of spatially neighboring, and preceding in decoding order, blocks of data. Such techniques are henceforth called “intra prediction” techniques. Note that in at least some cases, intra prediction is only using reference data from the current picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more than one of such techniques can be used in a given video coding technology, the technique in use can be coded in an intra prediction mode. In certain cases, modes can have submodes and/or parameters, and those can be coded individually or included in the mode codeword. Which codeword to use for a given mode/submode/parameter combination can have an impact in the coding efficiency gain through intra prediction, and so can the entropy coding technology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined in H.265, and further refined in newer coding technologies such as joint exploration model (JEM), versatile video coding (VVC), and benchmark set (BMS). A predictor block can be formed using neighboring sample values belonging to already available samples. Sample values of neighboring samples are copied into the predictor block according to a direction. A reference to the direction in use can be coded in the bitstream or may itself be predicted.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry. For example, the processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information indicates that a prediction of the current block is at least partially based on an inter prediction. Then, the processing circuitry reconstructs at least a sample of the current block as a combination of a result from the inter prediction and neighboring samples of the block that are selected based on a position of the sample.

In an embodiment, the prediction information is indicative of an intra-inter prediction mode that uses a combination of an intra prediction and the inter prediction of the current block, and the processing circuitry excludes a motion refinement based on a bi-directional optical flow from the inter prediction of the current block.

In some embodiments, the processing circuitry determines a usage of a position dependent prediction combination (PDPC) on the inter prediction based on the predication information, and reconstructs the sample in response to the determination of the usage of the PDPC on the inter prediction. In an example, the processing circuitry receives a flag that is indicative of the usage of the PDPC.

In some examples, the processing circuitry decodes a first flag for an intra-inter prediction mode that uses a combination of an intra prediction and the inter prediction of the current block, and decodes, when the first flag indicates a true for the intra-inter prediction mode, a second flag that is indicative of the usage of the PDPC. In an example, the processing circuitry decodes, based on a context model for an entropy coding, the second flag that is indicative of the usage of the PDPC.

In an embodiment, the processing circuitry applies a filter on the neighboring samples of the current block, and reconstructs the sample of the current block as a combination of the result from the inter prediction and the filtered neighboring samples of the current block.

In another embodiment, the processing circuitry reconstructs, the sample of the current block using the neighboring samples of the current block without an application of a filter on the neighboring samples.

In some examples, the processing circuitry determines whether the current block meets a block size condition that limits an application of the PDPC in a reconstruction of the current block, and excludes the application of the PDPC in a reconstruction of at least one sample of the current block when the block size condition is met. In an example, the block size condition depends on a size of a virtual process data unit.

In some examples, the processing circuitry disregards a neighboring sample in a calculation of the combination when a distance of the neighboring sample to the sample is larger than a threshold.

In some embodiments, the processing circuitry combines the result from the inter prediction with the neighboring samples that are selected based on the positon of the sample and reconstructed based on inter predictions.

In an example, the processing circuitry decodes a flag that is indicative of the usage of the PDPC when the prediction information is indicative of a merge mode.

In another example, the processing circuitry decodes, when a first flag is indicative of non-zero residue for the current block, a second flag that is indicative of the usage of the PDPC.

Aspects of the disclosure also provide a non-transitory computer-readable medium storing instructions which when executed by a computer for video decoding cause the computer to perform the method for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosed subject matter will be more apparent from the following detailed description and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of a communication system (100) in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of a communication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of a decoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of an encoder in accordance with an embodiment.

FIG. 5 shows a block diagram of an encoder in accordance with another embodiment.

FIG. 6 shows a block diagram of a decoder in accordance with another embodiment.

FIG. 7 shows an illustration of exemplary intra prediction directions and the intra prediction modes.

FIG. 8 shows an illustration of exemplary intra prediction directions and intra prediction modes in some examples.

FIGS. 9A-9B show weights for predicting samples according to some embodiments.

FIG. 10 shows an example of extended CU region in BDOF

FIG. 11 shows the diagonal split of a CU and the anti-diagonal split of a CU.

FIG. 12 shows a flow chart outlining a process example according to some embodiments.

FIG. 13 is a schematic illustration of a computer system in accordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a simplified block diagram of a communication system (100) according to an embodiment of the present disclosure. The communication system (100) includes a plurality of terminal devices that can communicate with each other, via, for example, a network (150). For example, the communication system (100) includes a first pair of terminal devices (110) and (120) interconnected via the network (150). In the FIG. 1 example, the first pair of terminal devices (110) and (120) performs unidirectional transmission of data. For example, the terminal device (110) may code video data (e.g., a stream of video pictures that are captured by the terminal device (110)) for transmission to the other terminal device (120) via the network (150). The encoded video data can be transmitted in the form of one or more coded video bitstreams. The terminal device (120) may receive the coded video data from the network (150), decode the coded video data to recover the video pictures and display video pictures according to the recovered video data. Unidirectional data transmission may be common in media serving applications and the like.

In another example, the communication system (100) includes a second pair of terminal devices (130) and (140) that performs bidirectional transmission of coded video data that may occur, for example, during videoconferencing. For bidirectional transmission of data, in an example, each terminal device of the terminal devices (130) and (140) may code video data (e.g., a stream of video pictures that are captured by the terminal device) for transmission to the other terminal device of the terminal devices (130) and (140) via the network (150). Each terminal device of the terminal devices (130) and (140) also may receive the coded video data transmitted by the other terminal device of the terminal devices (130) and (140), and may decode the coded video data to recover the video pictures and may display video pictures at an accessible display device according to the recovered video data.

In the FIG. 1 example, the terminal devices (110), (120), (130) and (140) may be illustrated as servers, personal computers and smart phones but the principles of the present disclosure may be not so limited. Embodiments of the present disclosure find application with laptop computers, tablet computers, media players and/or dedicated video conferencing equipment. The network (150) represents any number of networks that convey coded video data among the terminal devices (110), (120), (130) and (140), including for example wireline (wired) and/or wireless communication networks. The communication network (150) may exchange data in circuit-switched and/or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks and/or the Internet. For the purposes of the present discussion, the architecture and topology of the network (150) may be immaterial to the operation of the present disclosure unless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosed subject matter, the placement of a video encoder and a video decoder in a streaming environment. The disclosed subject matter can be equally applicable to other video enabled applications, including, for example, video conferencing, digital TV, storing of compressed video on digital media including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that can include a video source (201), for example a digital camera, creating for example a stream of video pictures (202) that are uncompressed. In an example, the stream of video pictures (202) includes samples that are taken by the digital camera. The stream of video pictures (202), depicted as a bold line to emphasize a high data volume when compared to encoded video data (204) (or coded video bitstreams), can be processed by an electronic device (220) that includes a video encoder (203) coupled to the video source (201). The video encoder (203) can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter as described in more detail below. The encoded video data (204) (or encoded video bitstream (204)), depicted as a thin line to emphasize the lower data volume when compared to the stream of video pictures (202), can be stored on a streaming server (205) for future use. One or more streaming client subsystems, such as client subsystems (206) and (208) in FIG. 2 can access the streaming server (205) to retrieve copies (207) and (209) of the encoded video data (204). A client subsystem (206) can include a video decoder (210), for example, in an electronic device (230). The video decoder (210) decodes the incoming copy (207) of the encoded video data and creates an outgoing stream of video pictures (211) that can be rendered on a display (212) (e.g., display screen) or other rendering device (not depicted). In some streaming systems, the encoded video data (204), (207), and (209) (e.g., video bitstreams) can be encoded according to certain video coding/compression standards. Examples of those standards include ITU-T Recommendation H.265. In an example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (220) and (230) can include other components (not shown). For example, the electronic device (220) can include a video decoder (not shown) and the electronic device (230) can include a video encoder (not shown) as well.

FIG. 3 shows a block diagram of a video decoder (310) according to an embodiment of the present disclosure. The video decoder (310) can be included in an electronic device (330). The electronic device (330) can include a receiver (331) (e.g., receiving circuitry). The video decoder (310) can be used in the place of the video decoder (210) in the FIG. 2 example.

The receiver (331) may receive one or more coded video sequences to be decoded by the video decoder (310); in the same or another embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent from other coded video sequences. The coded video sequence may be received from a channel (301), which may be a hardware/software link to a storage device which stores the encoded video data. The receiver (331) may receive the encoded video data with other data, for example, coded audio data and/or ancillary data streams, that may be forwarded to their respective using entities (not depicted). The receiver (331) may separate the coded video sequence from the other data. To combat network jitter, a buffer memory (315) may be coupled in between the receiver (331) and an entropy decoder/parser (320) (“parser (320)” henceforth). In certain applications, the buffer memory (315) is part of the video decoder (310). In others, it can be outside of the video decoder (310) (not depicted). In still others, there can be a buffer memory (not depicted) outside of the video decoder (310), for example to combat network jitter, and in addition another buffer memory (315) inside the video decoder (310), for example to handle playout timing. When the receiver (331) is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (315) may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer memory (315) may be required, can be comparatively large and can be advantageously of adaptive size, and may at least partially be implemented in an operating system or similar elements (not depicted) outside of the video decoder (310).

The video decoder (310) may include the parser (320) to reconstruct symbols (321) from the coded video sequence. Categories of those symbols include information used to manage operation of the video decoder (310), and potentially information to control a rendering device such as a render device (312) (e.g., a display screen) that is not an integral part of the electronic device (330) but can be coupled to the electronic device (330), as was shown in FIG. 3. The control information for the rendering device(s) may be in the form of Supplemental Enhancement Information (SEI messages) or Video Usability Information (VUI) parameter set fragments (not depicted). The parser (320) may parse/entropy-decode the coded video sequence that is received. The coding of the coded video sequence can be in accordance with a video coding technology or standard, and can follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, and so forth. The parser (320) may extract from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based upon at least one parameter corresponding to the group. Subgroups can include Groups of Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and so forth. The parser (320) may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, motion vectors, and so forth.

The parser (320) may perform an entropy decoding/parsing operation on the video sequence received from the buffer memory (315), so as to create symbols (321).

Reconstruction of the symbols (321) can involve multiple different units depending on the type of the coded video picture or parts thereof (such as: inter and intra picture, inter and intra block), and other factors. Which units are involved, and how, can be controlled by the subgroup control information that was parsed from the coded video sequence by the parser (320). The flow of such subgroup control information between the parser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (310) can be conceptually subdivided into a number of functional units as described below. In a practical implementation operating under commercial constraints, many of these units interact closely with each other and can, at least partly, be integrated into each other. However, for the purpose of describing the disclosed subject matter, the conceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). The scaler/inverse transform unit (351) receives a quantized transform coefficient as well as control information, including which transform to use, block size, quantization factor, quantization scaling matrices, etc. as symbol(s) (321) from the parser (320). The scaler/inverse transform unit (351) can output blocks comprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351) can pertain to an intra coded block; that is: a block that is not using predictive information from previously reconstructed pictures, but can use predictive information from previously reconstructed parts of the current picture. Such predictive information can be provided by an intra picture prediction unit (352). In some cases, the intra picture prediction unit (352) generates a block of the same size and shape of the block under reconstruction, using surrounding already reconstructed information fetched from the current picture buffer (358). The current picture buffer (358) buffers, for example, partly reconstructed current picture and/or fully reconstructed current picture. The aggregator (355), in some cases, adds, on a per sample basis, the prediction information the intra prediction unit (352) has generated to the output sample information as provided by the scaler/inverse transform unit (351).

In other cases, the output samples of the scaler/inverse transform unit (351) can pertain to an inter coded, and potentially motion compensated block. In such a case, a motion compensation prediction unit (353) can access reference picture memory (357) to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols (321) pertaining to the block, these samples can be added by the aggregator (355) to the output of the scaler/inverse transform unit (351) (in this case called the residual samples or residual signal) so as to generate output sample information. The addresses within the reference picture memory (357) from where the motion compensation prediction unit (353) fetches prediction samples can be controlled by motion vectors, available to the motion compensation prediction unit (353) in the form of symbols (321) that can have, for example X, Y, and reference picture components. Motion compensation also can include interpolation of sample values as fetched from the reference picture memory (357) when sub-sample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to various loop filtering techniques in the loop filter unit (356). Video compression technologies can include in-loop filter technologies that are controlled by parameters included in the coded video sequence (also referred to as coded video bitstream) and made available to the loop filter unit (356) as symbols (321) from the parser (320), but can also be responsive to meta-information obtained during the decoding of previous (in decoding order) parts of the coded picture or coded video sequence, as well as responsive to previously reconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that can be output to the render device (312) as well as stored in the reference picture memory (357) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used as reference pictures for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture has been identified as a reference picture (by, for example, the parser (320)), the current picture buffer (358) can become a part of the reference picture memory (357), and a fresh current picture buffer can be reallocated before commencing the reconstruction of the following coded picture.

The video decoder (310) may perform decoding operations according to a predetermined video compression technology in a standard, such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technology or standard being used, in the sense that the coded video sequence adheres to both the syntax of the video compression technology or standard and the profiles as documented in the video compression technology or standard. Specifically, a profile can select certain tools as the only tools available for use under that profile from all the tools available in the video compression technology or standard. Also necessary for compliance can be that the complexity of the coded video sequence is within bounds as defined by the level of the video compression technology or standard. In some cases, levels restrict the maximum picture size, maximum frame rate, maximum reconstruction sample rate (measured in, for example megasamples per second), maximum reference picture size, and so on. Limits set by levels can, in some cases, be further restricted through Hypothetical Reference Decoder (HRD) specifications and metadata for HRD buffer management signaled in the coded video sequence.

In an embodiment, the receiver (331) may receive additional (redundant) data with the encoded video. The additional data may be included as part of the coded video sequence(s). The additional data may be used by the video decoder (310) to properly decode the data and/or to more accurately reconstruct the original video data. Additional data can be in the form of, for example, temporal, spatial, or signal noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, and so on.

FIG. 4 shows a block diagram of a video encoder (403) according to an embodiment of the present disclosure. The video encoder (403) is included in an electronic device (420). The electronic device (420) includes a transmitter (440) (e.g., transmitting circuitry). The video encoder (403) can be used in the place of the video encoder (203) in the FIG. 2 example.

The video encoder (403) may receive video samples from a video source (401) (that is not part of the electronic device (420) in the FIG. 4 example) that may capture video image(s) to be coded by the video encoder (403). In another example, the video source (401) is a part of the electronic device (420).

The video source (401) may provide the source video sequence to be coded by the video encoder (403) in the form of a digital video sample stream that can be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ), and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (401) may be a storage device storing previously prepared video. In a videoconferencing system, the video source (401) may be a camera that captures local image information as a video sequence. Video data may be provided as a plurality of individual pictures that impart motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, wherein each pixel can comprise one or more samples depending on the sampling structure, color space, etc. in use. A person skilled in the art can readily understand the relationship between pixels and samples. The description below focuses on samples.

According to an embodiment, the video encoder (403) may code and compress the pictures of the source video sequence into a coded video sequence (443) in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed is one function of a controller (450). In some embodiments, the controller (450) controls other functional units as described below and is functionally coupled to the other functional units. The coupling is not depicted for clarity. Parameters set by the controller (450) can include rate control related parameters (picture skip, quantizer, lambda value of rate-distortion optimization techniques, . . . ), picture size, group of pictures (GOP) layout, maximum motion vector search range, and so forth. The controller (450) can be configured to have other suitable functions that pertain to the video encoder (403) optimized for a certain system design.

In some embodiments, the video encoder (403) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (430) (e.g., responsible for creating symbols, such as a symbol stream, based on an input picture to be coded, and a reference picture(s)), and a (local) decoder (433) embedded in the video encoder (403). The decoder (433) reconstructs the symbols to create the sample data in a similar manner as a (remote) decoder also would create (as any compression between symbols and coded video bitstream is lossless in the video compression technologies considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to the reference picture memory (434). As the decoding of a symbol stream leads to bit-exact results independent of decoder location (local or remote), the content in the reference picture memory (434) is also bit exact between the local encoder and remote encoder. In other words, the prediction part of an encoder “sees” as reference picture samples exactly the same sample values as a decoder would “see” when using prediction during decoding. This fundamental principle of reference picture synchronicity (and resulting drift, if synchronicity cannot be maintained, for example because of channel errors) is used in some related arts as well.

The operation of the “local” decoder (433) can be the same as of a “remote” decoder, such as the video decoder (310), which has already been described in detail above in conjunction with FIG. 3. Briefly referring also to FIG. 3, however, as symbols are available and encoding/decoding of symbols to a coded video sequence by an entropy coder (445) and the parser (320) can be lossless, the entropy decoding parts of the video decoder (310), including the buffer memory (315), and parser (320) may not be fully implemented in the local decoder (433).

An observation that can be made at this point is that any decoder technology except the parsing/entropy decoding that is present in a decoder also necessarily needs to be present, in substantially identical functional form, in a corresponding encoder. For this reason, the disclosed subject matter focuses on decoder operation. The description of encoder technologies can be abbreviated as they are the inverse of the comprehensively described decoder technologies. Only in certain areas a more detail description is required and provided below.

During operation, in some examples, the source coder (430) may perform motion compensated predictive coding, which codes an input picture predictively with reference to one or more previously-coded picture from the video sequence that were designated as “reference pictures”. In this manner, the coding engine (432) codes differences between pixel blocks of an input picture and pixel blocks of reference picture(s) that may be selected as prediction reference(s) to the input picture.

The local video decoder (433) may decode coded video data of pictures that may be designated as reference pictures, based on symbols created by the source coder (430). Operations of the coding engine (432) may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown in FIG. 4), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder (433) replicates decoding processes that may be performed by the video decoder on reference pictures and may cause reconstructed reference pictures to be stored in the reference picture cache (434). In this manner, the video encoder (403) may store copies of reconstructed reference pictures locally that have common content as the reconstructed reference pictures that will be obtained by a far-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the coding engine (432). That is, for a new picture to be coded, the predictor (435) may search the reference picture memory (434) for sample data (as candidate reference pixel blocks) or certain metadata such as reference picture motion vectors, block shapes, and so on, that may serve as an appropriate prediction reference for the new pictures. The predictor (435) may operate on a sample block-by-pixel block basis to find appropriate prediction references. In some cases, as determined by search results obtained by the predictor (435), an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (434).

The controller (450) may manage coding operations of the source coder (430), including, for example, setting of parameters and subgroup parameters used for encoding the video data.

Output of all aforementioned functional units may be subjected to entropy coding in the entropy coder (445). The entropy coder (445) translates the symbols as generated by the various functional units into a coded video sequence, by lossless compressing the symbols according to technologies such as Huffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as created by the entropy coder (445) to prepare for transmission via a communication channel (460), which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter (440) may merge coded video data from the video coder (403) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

The controller (450) may manage operation of the video encoder (403). During coding, the controller (450) may assign to each coded picture a certain coded picture type, which may affect the coding techniques that may be applied to the respective picture. For example, pictures often may be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decoded without using any other picture in the sequence as a source of prediction. Some video codecs allow for different types of intra pictures, including, for example Independent Decoder Refresh (“IDR”) Pictures. A person skilled in the art is aware of those variants of I pictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most one motion vector and reference index to predict the sample values of each block.

A bi-directionally predictive picture (B Picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most two motion vectors and reference indices to predict the sample values of each block. Similarly, multiple-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality of sample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 samples each) and coded on a block-by-block basis. Blocks may be coded predictively with reference to other (already coded) blocks as determined by the coding assignment applied to the blocks' respective pictures. For example, blocks of I pictures may be coded non-predictively or they may be coded predictively with reference to already coded blocks of the same picture (spatial prediction or intra prediction). Pixel blocks of P pictures may be coded predictively, via spatial prediction or via temporal prediction with reference to one previously coded reference picture. Blocks of B pictures may be coded predictively, via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures.

The video encoder (403) may perform coding operations according to a predetermined video coding technology or standard, such as ITU-T Rec. H.265. In its operation, the video encoder (403) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. The coded video data, therefore, may conform to a syntax specified by the video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional data with the encoded video. The source coder (430) may include such data as part of the coded video sequence. Additional data may comprise temporal/spatial/SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, and so on.

A video may be captured as a plurality of source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often abbreviated to intra prediction) makes use of spatial correlation in a given picture, and inter-picture prediction makes uses of the (temporal or other) correlation between the pictures. In an example, a specific picture under encoding/decoding, which is referred to as a current picture, is partitioned into blocks. When a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture can be coded by a vector that is referred to as a motion vector. The motion vector points to the reference block in the reference picture, and can have a third dimension identifying the reference picture, in case multiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in the inter-picture prediction. According to the bi-prediction technique, two reference pictures, such as a first reference picture and a second reference picture that are both prior in decoding order to the current picture in the video (but may be in the past and future, respectively, in display order) are used. A block in the current picture can be coded by a first motion vector that points to a first reference block in the first reference picture, and a second motion vector that points to a second reference block in the second reference picture. The block can be predicted by a combination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-picture prediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such as inter-picture predictions and intra-picture predictions are performed in the unit of blocks. For example, according to the HEVC standard, a picture in a sequence of video pictures is partitioned into coding tree units (CTU) for compression, the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), which are one luma CTB and two chroma CTBs. Each CTU can be recursively quadtree split into one or multiple coding units (CUs). For example, a CTU of 64×64 pixels can be split into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter prediction type or an intra prediction type. The CU is split into one or more prediction units (PUs) depending on the temporal and/or spatial predictability. Generally, each PU includes a luma prediction block (PB), and two chroma PBs. In an embodiment, a prediction operation in coding (encoding/decoding) is performed in the unit of a prediction block. Using a luma prediction block as an example of a prediction block, the prediction block includes a matrix of values (e.g., luma values) for pixels, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 5 shows a diagram of a video encoder (503) according to another embodiment of the disclosure. The video encoder (503) is configured to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a sequence of video pictures, and encode the processing block into a coded picture that is part of a coded video sequence. In an example, the video encoder (503) is used in the place of the video encoder (203) in the FIG. 2 example.

In an HEVC example, the video encoder (503) receives a matrix of sample values for a processing block, such as a prediction block of 8×8 samples, and the like. The video encoder (503) determines whether the processing block is best coded using intra mode, inter mode, or bi-prediction mode using, for example, rate-distortion optimization. When the processing block is to be coded in intra mode, the video encoder (503) may use an intra prediction technique to encode the processing block into the coded picture; and when the processing block is to be coded in inter mode or bi-prediction mode, the video encoder (503) may use an inter prediction or bi-prediction technique, respectively, to encode the processing block into the coded picture. In certain video coding technologies, merge mode can be an inter picture prediction submode where the motion vector is derived from one or more motion vector predictors without the benefit of a coded motion vector component outside the predictors. In certain other video coding technologies, a motion vector component applicable to the subject block may be present. In an example, the video encoder (503) includes other components, such as a mode decision module (not shown) to determine the mode of the processing blocks.

In the FIG. 5 example, the video encoder (503) includes the inter encoder (530), an intra encoder (522), a residue calculator (523), a switch (526), a residue encoder (524), a general controller (521), and an entropy encoder (525) coupled together as shown in FIG. 5.

The inter encoder (530) is configured to receive the samples of the current block (e.g., a processing block), compare the block to one or more reference blocks in reference pictures (e.g., blocks in previous pictures and later pictures), generate inter prediction information (e.g., description of redundant information according to inter encoding technique, motion vectors, merge mode information), and calculate inter prediction results (e.g., predicted block) based on the inter prediction information using any suitable technique. In some examples, the reference pictures are decoded reference pictures that are decoded based on the encoded video information.

The intra encoder (522) is configured to receive the samples of the current block (e.g., a processing block), in some cases compare the block to blocks already coded in the same picture, generate quantized coefficients after transform, and in some cases also intra prediction information (e.g., an intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (522) also calculates intra prediction results (e.g., predicted block) based on the intra prediction information and reference blocks in the same picture.

The general controller (521) is configured to determine general control data and control other components of the video encoder (503) based on the general control data. In an example, the general controller (521) determines the mode of the block, and provides a control signal to the switch (526) based on the mode. For example, when the mode is the intra mode, the general controller (521) controls the switch (526) to select the intra mode result for use by the residue calculator (523), and controls the entropy encoder (525) to select the intra prediction information and include the intra prediction information in the bitstream; and when the mode is the inter mode, the general controller (521) controls the switch (526) to select the inter prediction result for use by the residue calculator (523), and controls the entropy encoder (525) to select the inter prediction information and include the inter prediction information in the bitstream.

The residue calculator (523) is configured to calculate a difference (residue data) between the received block and prediction results selected from the intra encoder (522) or the inter encoder (530). The residue encoder (524) is configured to operate based on the residue data to encode the residue data to generate the transform coefficients. In an example, the residue encoder (524) is configured to convert the residue data from a spatial domain to a frequency domain, and generate the transform coefficients. The transform coefficients are then subject to quantization processing to obtain quantized transform coefficients. In various embodiments, the video encoder (503) also includes a residue decoder (528). The residue decoder (528) is configured to perform inverse-transform, and generate the decoded residue data. The decoded residue data can be suitably used by the intra encoder (522) and the inter encoder (530). For example, the inter encoder (530) can generate decoded blocks based on the decoded residue data and inter prediction information, and the intra encoder (522) can generate decoded blocks based on the decoded residue data and the intra prediction information. The decoded blocks are suitably processed to generate decoded pictures and the decoded pictures can be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

The entropy encoder (525) is configured to format the bitstream to include the encoded block. The entropy encoder (525) is configured to include various information according to a suitable standard, such as the HEVC standard. In an example, the entropy encoder (525) is configured to include the general control data, the selected prediction information (e.g., intra prediction information or inter prediction information), the residue information, and other suitable information in the bitstream. Note that, according to the disclosed subject matter, when coding a block in the merge submode of either inter mode or bi-prediction mode, there is no residue information.

FIG. 6 shows a diagram of a video decoder (610) according to another embodiment of the disclosure. The video decoder (610) is configured to receive coded pictures that are part of a coded video sequence, and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (610) is used in the place of the video decoder (210) in the FIG. 2 example.

In the FIG. 6 example, the video decoder (610) includes an entropy decoder (671), an inter decoder (680), a residue decoder (673), a reconstruction module (674), and an intra decoder (672) coupled together as shown in FIG. 6.

The entropy decoder (671) can be configured to reconstruct, from the coded picture, certain symbols that represent the syntax elements of which the coded picture is made up. Such symbols can include, for example, the mode in which a block is coded (such as, for example, intra mode, inter mode, bi-predicted mode, the latter two in merge submode or another submode), prediction information (such as, for example, intra prediction information or inter prediction information) that can identify certain sample or metadata that is used for prediction by the intra decoder (672) or the inter decoder (680), respectively, residual information in the form of, for example, quantized transform coefficients, and the like. In an example, when the prediction mode is inter or bi-predicted mode, the inter prediction information is provided to the inter decoder (680); and when the prediction type is the intra prediction type, the intra prediction information is provided to the intra decoder (672). The residual information can be subject to inverse quantization and is provided to the residue decoder (673).

The inter decoder (680) is configured to receive the inter prediction information, and generate inter prediction results based on the inter prediction information.

The intra decoder (672) is configured to receive the intra prediction information, and generate prediction results based on the intra prediction information.

The residue decoder (673) is configured to perform inverse quantization to extract de-quantized transform coefficients, and process the de-quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residue decoder (673) may also require certain control information (to include the Quantizer Parameter (QP)), and that information may be provided by the entropy decoder (671) (data path not depicted as this may be low volume control information only).

The reconstruction module (674) is configured to combine, in the spatial domain, the residual as output by the residue decoder (673) and the prediction results (as output by the inter or intra prediction modules as the case may be) to form a reconstructed block, that may be part of the reconstructed picture, which in turn may be part of the reconstructed video. It is noted that other suitable operations, such as a deblocking operation and the like, can be performed to improve the visual quality.

It is noted that the video encoders (203), (403), and (503), and the video decoders (210), (310), and (610) can be implemented using any suitable technique. In an embodiment, the video encoders (203), (403), and (503), and the video decoders (210), (310), and (610) can be implemented using one or more integrated circuits. In another embodiment, the video encoders (203), (403), and (403), and the video decoders (210), (310), and (610) can be implemented using one or more processors that execute software instructions.

Aspects of the disclosure provide enhancement for position dependent prediction combination. In various embodiments, a set of advanced video coding technologies, specifically enhanced schemes for intra-inter prediction mode, is provided in the present disclosure.

FIG. 7 shows an illustration of exemplary intra prediction directions and the intra prediction modes used in HEVC. In HEVC, there are total 35 intra prediction modes (mode 0 to mode 34). The mode 0 and mode 1 are non-directional modes, among which mode 0 is planar mode and mode 1 is DC mode. The modes 2-34 are directional modes, among which mode 10 is horizontal mode, mode 26 is vertical mode, and mode 2, mode 18 and mode 34 are diagonal modes. In some examples, the intra prediction modes are signaled by three most probable modes (MPMs) and 32 remaining modes.

FIG. 8 shows an illustration of exemplary intra prediction directions and intra prediction modes in some examples (e.g., VVC). There are total 87 intra prediction modes (mode −10 to mode 76), among which mode 18 is horizontal mode, mode 50 is vertical mode, and mode 2, mode 34 and mode 66 are diagonal modes. Modes −1˜−10 and Modes 67˜76 are called wide-angle intra prediction (WAIP) modes.

In some examples, the HEVC style intra prediction is based on filtered reference samples. For example, when the intra prediction mode is not any of the DC mode and the planar mode, a filter is applied to the boundary reference samples, and the filtered reference samples are used to predict values in the current block based on the intra prediction mode.

In some examples, PDPC combines the boundary reference samples and HEVC style intra prediction. In some embodiments, PDPC is applied to the following intra modes without signaling: planar, DC, WAIP modes, horizontal, vertical, bottom-left angular mode (mode 2) and its 8 adjacent angular modes (mode 3˜10), and top-right angular mode (mode 66) and its 8 adjacent angular modes (mode 58˜65).

In an example, the prediction sample pred′[x][y] located at position (x, y) is predicted using an intra prediction mode (DC, planar, angular) and a linear combination of reference samples according to Eq. 1:

pred′[x][y]=(wL×R(−1,y)+wT×R(x,−1)−wTL×R(−1,−1)+(64−wL−wT+wTL)×pred[x][y]+32)>>6  (Eq. 1)

where R(x,−1), R(−1,y) represent the (unfiltered) reference samples located at top and left of current sample (x, y), respectively, R(−1,−1) represents the reference sample located at the top-left corner of the current block, and wT, wL, and wTL denote weights. For the DC mode the weights are calculated by Eq. 2-Eq. 5, width denotes the width of the current block, and height denotes the height of the current block:

wT=32>>((y<<1)>>nScale)  (Eq. 2)

wL=32>>((x<<1)>>nScale)  (Eq. 3)

wTL=(wL>>4)+(wT>>4)  (Eq. 4)

nScale=(log 2(width)+log 2(height)−2)>>2  (Eq. 5)

where wT denotes the weighting factor for the reference sample located in the above reference line with the same horizontal coordinate, wL denotes the weighting factor for the reference sample located in the left reference line with the same vertical coordinate, and wTL denotes the weighting factor for the top-left reference sample of the current block, nScale specifies how fast weighting factors decrease along the axis (wL decreasing from left to right or wT decreasing from top to bottom), namely weighting factor decrement rate, and it is the same along x-axis (from left to right) and y-axis (from top to bottom) in current design. And 32 denotes the initial weighting factors for the neighboring samples, and the initial weighting factor is also the top (left or top-left) weightings assigned to top-left sample in current CB, and the weighting factors of neighboring samples in PDPC process should be equal to or less than this initial weighting factor.

For the planar mode, wTL=0; while for horizontal mode, wTL=wT; and for vertical mode wTL=wL. The PDPC weights can be calculated with add operations and shift operations. The value of pred′[x][y] can be computed in a single step using Eq. 1.

FIG. 9A shows weights for prediction sample at (0, 0) in DC mode. In the FIG. 9A example, the current block is a 4×4 block, width is 4, height is also 4, thus nScale is 0. Then, wT is 32, wL is 32, and −wTL is −4.

FIG. 9B shows weights for prediction sample at (1,0) in DC mode. In the FIG. 9B example, the current block is a 4×4 block, width is 4, height is also 4, thus nScale is 0. Then, wT is 32, wL is 8, and −wTL is −2.

When PDPC is applied to DC, planar, horizontal, and vertical intra modes, additional boundary filters are not needed, such as the HEVC DC mode boundary filter or horizontal/vertical mode edge filters. For example, PDPC combines the un-filtered boundary reference samples and HEVC style intra prediction with filtered boundary reference samples.

More generally, in some examples, inputs to the PDPC process includes:

the intra prediction mode that is represented by predModeIntra;

the width of the current block that is represented nTbW;

the height of the current block that is represented by nTbH;

the width of the reference samples that is represented by refW;

the height of the reference samples that is represented by refH;

the predicted samples by HEVC style intra prediction that are represented by predSamples[x][y], with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;

the unfiltered reference (also referred to as neighboring) samples p[x][y], with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1; and

the colour component of the current block that is represented by cIdx.

Further, the outputs of the PDPC process are the modified predicted samples predSamples′[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

Then, a scaling factor nScale is calculated by Eq. 6 which is similar to Eq. 5:

((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 6)

Further, a reference sample array mainRef[x] with x=0 . . . refW is defined as the array of unfiltered reference samples above the current block and another reference sample array sideRef[y] with y=0 . . . refH is defined as the array of unfiltered reference samples to the left of the current block, and can be derived from unfiltered reference samples according to Eq. 7 and Eq. 8:

mainRef[x]=p[x][−1]  (Eq. 7)

sideRef[y]=p[−1][y]  (Eq. 8)

For each location (x,y) in the current block, the PDPC calculation uses a reference sample at the top that is denoted as refT[x][y], a reference sample at the left that is denoted as refL[x][y], and a reference sample at the corner p[−1,−1]. In some examples, the modified predicted sample is calculated by Eq. 9 in some examples, and the result is suitably clipped according to the cIdx variable that is indicative of the color component.

predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq. 9)

The reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL can be determined based on the intra prediction mode predModelIntra.

In an example, when the intra prediction mode predModeIntra is equal to INTRA PLANAR (e.g., 0, planar mode, mode 0), INTRA DC (e.g., 1, DC mode, mode 1), INTRA_ANGULAR18 (e.g., 18, horizontal mode, mode 18 in the case of 67 intra prediction modes), or INTRA_ANGULAR50 (e.g., 50, vertical mode, mode 50 in the case of 67 intra prediction modes), reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL can be determined according to Eq. 10-Eq. 14:

refL[x][y]=p[−1][y]  (Eq. 10)

refT[x][y]=p[x][−1]  (Eq. 11)

wT[y]=32>>((y<<1)>>nScale)  (Eq. 12)

wL[x]=32>>((x<<1)>>nScale)  (Eq. 13)

wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)):0  (Eq. 14)

In another example, when the intra prediction mode predModeIntra is equal to INTRA_ANGULAR2 (e.g., 2, mode 2 in the case of 67 intra prediction mode) or INTRA_ANGULAR66 (e.g., 66, mode 66 in the case of 66 intra prediction mode), reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL can be determined according to Eq. 15-Eq. 19:

refL[x][y]=p[−1][x+y+1]  (Eq. 15)

refT[x][y]=p[x+y+1][−1]  (Eq. 16)

wT[y]=32>>((y<<1)>>nScale)  (Eq. 17)

wL[x]=32>>((x<<1)>>nScale)  (Eq. 18)

wTL[x][y]=0  (Eq. 19)

In another example, when the intra prediction mode predModeIntra is less than or equal to INTRA_ANGULAR10 (e.g., 10, mode 10 in the case of 67 intra prediction mode), for location (x, y), variables dXPos[y], dXFrac[y], dXInt[y] and dX[y] are derived based on a variable invAngle that is a function of the intra prediction mode predModeIntra. In an example, the invAngle can be determined based on a look-up table that stores a corresponding invAngle value to each intra prediction mode, and then the reference samples refL[x][y], refL[x][y], and the weights wL, wT and wTL are determined based on the variables dXPos[y], dXFrac[y], dXInt[y] and dX[y].

For example, the variables dXPos[y], dXFrac[y], dXInt[y] and dX[y] are determined according to Eq. 20-23:

dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 20)

dXFrac[y]=dXPos[y]&63  (Eq. 21)

dXInt[y]=dXPos[y]>>6  (Eq. 22)

dX[y]=x+dXInt[y]  (Eq. 23)

Then, the reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL are determined according to Eq. 24-Eq. 28.

refL[x][y]=0  (Eq. 24)

refT[x][y]=(dX[y]<refW−1)?((64−dXFrac[y])×mainRef[dX[y]]+dXFrac[y]×mainRef[dX[y]+1]+32)>>6:0  (Eq. 25)

wT[y]=(dX[y]refW−1)?32>>((y<<1)>>nScale):0  (Eq. 26)

wL[x]=0  (Eq. 27)

wTL[x][y]=0  (Eq. 28)

In another example, when the intra prediction mode predModeIntra is greater than or equal to INTRA_ANGULAR58 (e.g., 58, mode 58 in the case of 67 intra prediction modes), variables dYPos[x], dYFrac[x], dYInt[x] and dY[x] are derived based on a variable invAngle that is a function of the intra prediction mode predModeIntra. In an example, the invAngle can be determined based on a look-up table that stores a corresponding invAngle value to each intra prediction mode, and then the reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL are determined based on the variables dYPos[x], dYFrac[x], dYInt[x] and dY[x].

For example, the variables dYPos[x], dYFrac[x], dYInt[x] and dY[x] are determined according to Eq. 29-33:

dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 29)

dYFrac[x]=dYPos[x]&63  (Eq. 30)

dYInt[x]=dYPos[x]>>6  (Eq. 31)

dY[x]=x+dYInt[x]  (Eq. 32)

Then, the reference samples refT[x][y], refL[x][y], and the weights wL, wT and wTL are determined according to Eq. 33-Eq. 37.

refL[x][y]=(dY[x]<refH−1)?((64−dYFrac[x])×sideRef[dY[x]]+dYFrac[x]×sideRef[dY[x]+1]+32)>>6:0  (Eq. 33)

refT[x][y]=0  (Eq. 34)

wT[y]=0  (Eq. 35)

wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale):0  (Eq. 36)

wTL[x][y]=0  (Eq. 37)

In some examples, when the variable predModeIntra is between 11-57 and is not one of 18 and 50, then the refL[x][y], refT[x][y], wT[y], wL[y] and wTL[x][y] are all set equal to 0. Then, the values of the filtered samples filtSamples[x][y], with x=0 . . . nTbW −1, y=0 . . . nTbH−1 are derived as follows:

filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 38)

It is noted that some PDPC processes include non-integer (e.g., floating point) operations that increase computation complexity. In some embodiments, the PDPC process includes relatively simple computations for the planar mode (mode 0), the DC mode (mode 1), the vertical mode (e.g., mode 50 in the case of 67 intra prediction modes), the horizontal mode (e.g., mode 18 in the case of 67 intra prediction modes), and the diagonal modes (e.g., mode 2, mode 66, and mode 34 in the case of 67 intra prediction modes), and the PDPC process includes relatively complex computations for the other modes.

In some embodiments, for the chroma component of an intra coded block, the encoder selects the best chroma prediction modes among five modes including planar mode (mode index 0), DC mode (mode index 1), horizontal mode (mode index 18), vertical mode (mode index 50), diagonal mode (mode index 66) and a direct copy of the intra prediction mode for the associated luma component, namely DM mode. The mapping between intra prediction direction and intra prediction mode number for chroma is shown in Table 1.

TABLE 1 Mapping between intra prediction direction and intra prediction mode for chroma IntraPredModeY[ xCb + cbWidth / 2 ] intra_chroma_pred_mode [ yCb + cbHeight / 2 ] [ xCb ][ yCb ] 0 50 18 1 X ( 0 <= X <= 66 ) 0 66 0 0 0 0 1 50 66 50 50 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

To avoid duplicate mode, in some embodiments, the four modes other than DM are assigned according the intra prediction modes of the associated luma components. When the intra prediction mode number for the chroma component is 4, the intra prediction direction for the luma component is used for the intra prediction sample generation for the chroma component. When the intra prediction mode number for the chroma component is not 4 and it is identical to the intra prediction mode number for the luma component, the intra prediction direction of 66 is used for the intra prediction sample generation for the chroma component.

According to some aspects of the disclosure, inter-picture prediction (also referred to as inter prediction) includes merge mode and skip mode.

In the merge mode for Inter-picture prediction, the motion data (e.g., motion vector) of a block is inferred instead of being explicitly signaled. In an example, a merge candidate list of candidate motion parameters is firstly constructed, then an index is signaled which identifies the candidate to be used.

In some embodiments, a merge candidate list includes a non sub-CU merge candidate list and a sub-CU merge candidate list. The non sub-CU merge candidates are constructed based on the spatial neighboring motion vectors, collocated temporal motion vectors, and history based motion vectors. The sub-CU Merge candidate list includes affine merge candidates and ATMVP merge candidates. The sub-CU merge candidate is used to derive multiple MVs for current CU and different part of the samples in current CU can have different motion vectors.

In the skip mode, the motion data of a block is inferred instead of being explicitly signaled and that the prediction residual is zero, i.e. no transform coefficients are transmitted. At the beginning of each CU in an inter-picture prediction slice, a skip flag is signaled. The skip flag indicates that the merge mode is used to derive the motion data, and no residual data is present in the coded video bitstream.

According to some aspects of the disclosure, intra and inter predictions can be suitably combined, such as a multi-hypothesis intra-inter prediction. The multi-hypothesis intra-inter prediction combines one intra prediction and one merge indexed prediction, and is referred to as intra-inter prediction mode in the present disclosure. In an example, when a CU is in the merge mode, a specific flag for intra mode is signaled. When the specific flag is true, an intra mode can be selected from an intra candidate list. For luma component, the intra candidate list is derived from 4 intra prediction modes including DC mode, planar mode, horizontal mode, and vertical mode, and the size of the intra mode candidate list can be 3 or 4 depending on the block shape. In an example, when the CU width is larger than twice of CU height, the horizontal mode is removed from the intra mode candidate list and when the CU height is larger than twice of CU width, vertical mode is removed from the intra mode candidate list. In some embodiments, an intra prediction is performed based on an intra prediction mode selected by an intra mode index and an inter prediction is performed based on a merge index. The intra prediction and the inter prediction are combined using weighted average. For chroma component, DM is always applied without extra signaling in some examples.

In some embodiments, the weights for combining the intra prediction and the inter prediction can be suitably determined. In an example, when DC or planar mode is selected or the Coding Block (CB) width or height is smaller than 4, equal weights are applied for inter prediction and intra prediction. In another example, for a CB with CB width and height larger than or equal to 4, when horizontal/vertical mode is selected, the CB is first vertically/horizontally split into four equal-area regions. Each region has a weight set, denoted as (w_intra_(i), w_inter_(i)), where i is from 1 to 4. In an example, the first weight set (w_intra₁, w_inter₁)=(6, 2), the second weight set (w_intra₂, w_inter₂)=(5, 3), the third weight set (w_intra₃, w_inter₃)=(3, 5), and fourth weight set (w_intra₄, w_inter₄)=(2, 6), can be applied to a corresponding region. For example, the first weight set (w_intra₁, w_inter₁) is for the region closest to the reference samples and fourth weight set (w_intra₄, w_inter₄) is for the region farthest away from the reference samples. Then, the combined prediction can be calculated by summing up the two weighted predictions and right-shifting 3 bits.

Moreover, the intra prediction mode for the intra hypothesis of predictors can be saved for the intra mode coding of the following neighboring CBs when the neighboring CBs are intra coded.

According to some aspects of the disclosure, a motion refinement technique that is referred to as bi-directional optical flow (BDOF) mode is used in inter prediction. BDOF is also referred to as BIO in some examples. BDOF is used to refine the bi-prediction signal of a CU at the 4×4 sub-block level. BDOF is applied to a CU when the CU satisfies the following conditions: 1) the CU's height is not 4, and the CU is not in size of 4×8, 2) the CU is not coded using affine mode or the ATMVP merge mode; 3) the CU is coded using “true” bi-prediction mode, i.e., one of the two reference pictures is prior to the current picture in display order and the other is after the current picture in display order. BDOF is only applied to the luma component in some examples.

The motion refinement in the BDOF mode is based on the optical flow concept, which assumes that the motion of an object is smooth. For each 4×4 sub-block, a motion refinement (v_(x), v_(y)) is calculated by minimizing the difference between the L0 and L1 prediction samples. The motion refinement is then used to adjust the bi-predicted sample values in the 4×4 sub-block. The following steps are applied in the BDOF process.

First, the horizontal and vertical gradients,

${\frac{\partial I^{(k)}}{\partial x}\left( {i,j} \right){and}\frac{\partial I^{(k)}}{\partial y}\left( {i,j} \right)},$

k=0,1, of the two prediction signals are computed by directly calculating the difference between two neighboring samples, i.e.

$\begin{matrix} {{{\frac{\partial I^{(k)}}{\partial x}\left( {i,j} \right)} = \left( {{I^{(k)}\left( {{i + 1},j} \right)} - {I^{(k)}\left( {{i - 1},j} \right)}} \right)}\operatorname{>>}4} & \left( {{Eq}.39} \right) \end{matrix}$ ${{\frac{\partial I^{(k)}}{\partial y}\left( {i,j} \right)} = \left( {{I^{(k)}\left( {i,{j + 1}} \right)} - {I^{(k)}\left( {i,{j - 1}} \right)}} \right)}\operatorname{>>}4$

where I^((k))(i,j) are the sample value at coordinate (i,j) of the prediction signal in list k, k=0,1.

Then, the auto- and cross-correlation of the gradients, S₁, S₂, S₃, S_(s) and S₆, are calculated as

$\begin{matrix} {{S_{1} = {\sum_{{({i,j})} \in \Omega}{{\psi_{x}\left( {i,j} \right)} \cdot {\psi_{x}\left( {i,j} \right)}}}},} & \left( {{Eq}.40} \right) \end{matrix}$ S₂ = ∑_((i, j) ∈ Ω)ψ_(x)(i, j) ⋅ ψ_(y)(i, j) S₃ = ∑_((i, j) ∈ Ω)θ(i, j) ⋅ ψ_(x)(i, j)

$\begin{matrix} {S_{5} = {\sum_{{({i,j})} \in \Omega}{{\psi_{y}\left( {i,j} \right)} \cdot {\psi_{y}\left( {i,j} \right)}}}} & \left( {{Eq}.41} \right) \end{matrix}$ $\begin{matrix} {S_{6} = {\sum_{{({i,j})} \in \Omega}{{\theta\left( {i,j} \right)} \cdot {\psi_{y}\left( {i,j} \right)}}}} &  \end{matrix}$ where ${{\psi_{x}\left( {i,j} \right)} = \left( {{\frac{\partial I^{(1)}}{\partial x}\left( {i,j} \right)} + {\frac{\partial I^{(0)}}{\partial x}\left( {i,j} \right)}} \right)}\operatorname{>>}n_{a}$ ${{\psi_{y}\left( {i,j} \right)} = \left( {{\frac{\partial I^{(1)}}{\partial y}\left( {i,j} \right)} + {\frac{\partial I^{(0)}}{\partial y}\left( {i,j} \right)}} \right)}\operatorname{>>}n_{a}$ θ(i, j) = (I⁽¹⁾(i, j)>> n_(b)) − (I⁽⁰⁾(i, j)>> n_(b))

where Ω is a 6×6 window around the 4×4 sub-block.

The motion refinement (v_(x), v_(y)) is then derived using the cross- and auto-correlation terms using the following:

$\begin{matrix} {v_{x} = {S_{1} > {{0?{clip}}3\left( {{- {th}_{BIO}^{\prime}},{th}_{BIO}^{\prime},{- \left( {\left( {S_{3} \cdot 2^{n_{b} - n_{a}}} \right)\operatorname{>>}\left\lfloor {\log_{2}S_{1}} \right\rfloor} \right)}} \right):0}}} & \left( {{Eq}.42} \right) \end{matrix}$ v_(y) = S₅ > 0?clip3(−th_(BIO)^(′), th_(BIO)^(′), −((S₆ ⋅ 2^(n_(b) − n_(a)) − ((v_(x)S_(2, m))(<< n)_(S₂) + v_(x)S_(2, s))/2)>> ⌊log₂S₅⌋)) : 0

Based on the motion refinement and the gradients, the following adjustment is calculated for each sample in the 4×4 sub-block:

$\begin{matrix} {{b\left( {x,y} \right)} = {{rn{d\left( {\left( {v_{z}\left( {\frac{\partial{I^{(1)}\left( {x,y} \right)}}{\partial x} - \frac{\partial{I^{(0)}\left( {x,y} \right)}}{\partial x}} \right)} \right)/2} \right)}} + {rn{d\left( {\left( {v_{y}\left( {\frac{\partial{I^{(1)}\left( {x,y} \right)}}{\partial y} - \frac{\partial{I^{(0)}\left( {x,y} \right)}}{\partial y}} \right)} \right)/2} \right)}}}} & \left( {{Eq}.43} \right) \end{matrix}$

Finally, the BDOF samples of the CU are calculated by adjusting the bi-prediction samples as follows:

pred_(BDOF)(x,y)=(I ⁽⁰⁾(x,y)+I ⁽¹⁾(x,y)+b(x,y)+o _(offset))>>shift  (Eq. 44)

In the above, the values of n_(a), n_(b) and n_(s) ₂ are equal to 3, 6, and 12, respectively. These values are selected such that the multipliers in the BDOF process do not exceed 15-bit, and the maximum bit-width of the intermediate parameters in the BDOF process is kept within 32-bit.

To derive the gradient values, some prediction samples I^((k))(i,j) in list k (k=0,1) outside of the current CU boundaries can be generated.

FIG. 10 shows an example of extended CU region in BDOF. In the FIG. 10 example, a 4×4 CU 1010 is shown as a shaded area. The BDOF uses one extended row/column around the CU's boundaries, and the extended area is shown as a 6×6 block 1020 of dashed line. To control the computational complexity of generating the out-of-boundary prediction samples, bilinear filter is used to generate prediction samples in the extended area (white positions), and the normal 8-tap motion compensation interpolation filter is used to generate prediction samples within the CU (gray positions). These extended sample values are used in gradient calculation only. For the remaining steps in the BDOF process, if any sample and gradient values outside of the CU boundaries are needed, they are padded (i.e. repeated) from their nearest neighbors.

In some examples, triangle partition can be used in inter prediction. For example (e.g., VTM3), a new triangle partition mode is introduced for inter prediction. The triangle partition mode is only applied to CUs that are 8×8 or larger and are coded in skip or merge mode. For a CU satisfying these conditions, a CU-level flag is signaled to indicate whether the triangle partition mode is applied or not.

When the triangular partition mode is used, a CU is split evenly into two triangle-shaped partitions, using either the diagonal split or the anti-diagonal split.

FIG. 11 shows the diagonal split of a CU and the anti-diagonal split of a CU.

Each triangle partition in a CU has its own motion information, and can be inter-predicted using its own motion. In an example, only uni-prediction is allowed for each triangle partition. Then each partition has one motion vector and one reference index. The uni-prediction motion constraint is applied to ensure that same as the conventional bi-prediction, only two motion compensated prediction are needed for each CU. The uni-prediction motion for each partition is derived from a uni-prediction candidate list constructed using the process.

In some examples, when a CU-level flag indicates that the current CU is coded using the triangle partition mode, then an index in the range of [0, 39] is further signaled. Using this triangle partition index, the direction of the triangle partition (diagonal or anti-diagonal), as well as the motion for each of the partitions can be obtained through a look-up table. After predicting each of the triangle partitions, the sample values along the diagonal or anti-diagonal edge are adjusted using a blending processing with adaptive weights. After the whole CU is predicted, the transform and quantization process will be applied to the whole CU as in other prediction modes. Finally, the motion field of a CU predicted using the triangle partition mode is stored in 4×4 units.

In some related examples of the intra-inter prediction mode, PDPC is only applied to intra prediction samples to improve video quality by reducing artifacts. In the related examples, there may still be some artifacts for intra-inter prediction samples, which may not be an optimal video result.

The proposed methods may be used separately or combined in any order.

According to some aspects of the disclosure, PDPC can be applied to inter prediction samples (or reconstructed samples of an inter coded CU), and using PDPC filtering techniques in inter prediction can be referred to as inter PDPC mode. In an example, Eq. 1 can be suitably modified for inter PDPC mode. For example, pred[x][y] is modified to denote inter prediction sample value in the inter PDPC mode.

In some examples, a flag, that is referred to as interPDPCFlag in the present disclosure (other suitable name can be used for the flag), is signaled to indicate whether to apply PDPC to inter prediction samples or not. In an example, when the flag interPDPCFlag is true, the inter prediction samples (or reconstructed samples of an inter coded CU) are further modified in a PDPC process in the similar manner as the PDPC process for the intra prediction.

In some embodiments, when multi-hypothesis intra-inter prediction flag is true, one additional flag, such as interPDPCFlag in the present disclosure, is signaled to indicate whether to apply multi-hypothesis intra-inter prediction or apply PDPC to inter prediction samples. In an example, when interPDPCFlag is true, PDPC is directly applied to inter prediction samples (or reconstructed samples of an inter coded CU) to generate the final inter prediction values (or reconstructed samples of an inter coded CU). Otherwise, multi-hypothesis intra-inter prediction is applied to inter prediction samples (or reconstructed samples of an inter coded CU) in an example.

In an embodiment, a fixed context model is used for the entropy coding of the interPDPCFlag.

In another embodiment, a selection of a context model used for entropy coding of the interPDPCFlag depends on the coded information, including but not limited to: whether neighboring CU is intra CU or inter CU or in intra-inter mode, the coding block size and the like. The block size may be measured by block area size, block width, block height, block width plus height, block width and height and the like.

For example, when none of the neighboring modes are intra coded CU, a first context model is used; otherwise, if at least one of the neighboring modes is intra coded CU, a second context model is used.

In another example, when none of the neighboring modes is intra coded CU, a first context model is used. If one of the neighboring modes is intra coded CU, a second context model is used. If more than one of the neighboring modes are intra coded CU, a third context model is used.

In another embodiment, when PDPC is applied to inter prediction samples, a smoothing filter is applied to neighboring reconstructed (or prediction) samples.

In another embodiment, to apply PDPC to inter prediction samples, the neighboring reconstructed (or prediction) samples are directly used for PDPC process without using a smoothing or interpolation filter.

In another embodiment, when the block size of current block is less than or equal to a threshold, the flag interPDPCFlag can be derived as false. The block size may be measured by block area size, block width, block height, block width plus height, block width and height, and the like. In an example, when the block area size is less than 64 samples, the flag interPDPCFlag is derived to be false.

In another embodiment, when the block size of the current block is larger than a threshold, such as the size of VPDU (virtual process data unit, defined as 64×64 block in an example), the flag interPDPCFlag is not signaled but can be inferred as false.

In another embodiment, PDPC scaling factor (e.g., nScale in the present disclosure) or weighting factor (e.g., weights in Eq. 1) are constrained such that when the distance of the current pixel to the reconstructed pixels (e.g., inputs to Eq. 1) is larger than a certain threshold, such as VPDU width/height, the PDPC (as a filtering technique) will not change the value of the current pixel.

In some embodiments, to apply PDPC to inter prediction samples (or reconstructed samples of an inter coded CU), a default intra prediction mode is assigned to current block, so that the associated parameters of the default mode, such as weighting factors and scaling factor, can be used for PDPC process. In an example, the default intra prediction mode can be planar mode, or DC mode. In another example, the default intra prediction mode for chroma component is DM prediction mode. In another example, the subsequent blocks can use this default intra prediction mode for the intra mode coding and Most Probable Mode (MPM) derivation.

In another embodiment, to apply PDPC to inter prediction samples, BDOF (or referred to as BIO) is not applied in the process of generating inter prediction samples.

In another embodiment, when PDPC is applied to inter prediction samples, only the neighboring reconstructed (or prediction) samples from inter coded CU can be used for PDPC process in an example.

In another embodiment, interPDPCFlag is signaled for a coding block coded in merge mode. In another embodiment, PDPC is not applied to skip mode CU nor sub-block merge mode CU. In another embodiment, PDPC is not applied to triangle partition mode coded CU.

In another embodiment, interPDPCFlag is signaled at the TU level, and is only signaled when the CBF (coded block flag) of current TU is not zero. In an example, th flag interPDPCFlag is not signaled and can be inferred as zero (false) when CBF of current TU is zero. In another example, the neighboring reconstructed samples of current TU (or current PU/CU) can be used for PDPC.

In another embodiment, to apply PDPC to inter prediction samples, only uni-prediction motion vector can be used to generate the intra prediction samples. When the motion vector of current block is bi-prediction motion vector, the motion vector needs to be converted to uni-prediction motion vector. In an example, when the motion vector of current block is bi-prediction motion vector, the motion vector in List 1 is discarded, and the motion vector in List 0 can be used to generate the intra prediction samples.

In another embodiment, to apply PDPC to inter prediction samples, transform skip mode (TSM) is not applied or signaled.

In some embodiments, BDOF is not applied to the inter prediction samples when intra-inter mode is true.

In some embodiments, when bi-prediction is applied, boundary filtering can be applied to both forward and backward prediction blocks using their spatially neighboring samples in the corresponding reference picture. Then, a bi-prediction block is generated by averaging (or weighted sum) of forward and backward prediction blocks. In an example, the boundary filtering is applied using a PDPC filter. In another example, the neighboring samples of a forward (or backward) prediction block may include the top, left, bottom and right spatially neighboring samples in the associated reference picture.

In some embodiments, when uni-prediction is applied, filtering is applied to the prediction block using its spatially neighboring samples in the reference picture. In an example, the boundary filtering is applied using a PDPC filter. In another, the neighboring samples of a forward (or backward) prediction block may include the top, left, bottom and right spatially neighboring samples in the associated reference picture.

In some embodiments, planar prediction is applied to the inter prediction blocks using their spatially neighboring samples in the corresponding reference picture. This process is named as inter prediction sample refining process. In an example, when bi-prediction is applied, after the inter prediction refining process, a bi-prediction block is generated by averaging (or weighted sum) of forward and backward refined prediction blocks. In another example, the neighboring samples used for inter prediction refining process may include the top, left, bottom and right spatially neighboring samples in the associated reference picture.

FIG. 12 shows a flow chart outlining a process (1200) according to an embodiment of the disclosure. The process (1200) can be used in the reconstruction of a block, so to generate a prediction block for the block under reconstruction. In various embodiments, the process (1200) are executed by processing circuitry, such as the processing circuitry in the terminal devices (110), (120), (130) and (140), the processing circuitry that performs functions of the video encoder (203), the processing circuitry that performs functions of the video decoder (210), the processing circuitry that performs functions of the video decoder (310), the processing circuitry that performs functions of the video encoder (403), and the like. In some embodiments, the process (1200) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (1200). The process starts at (S1201) and proceeds to (S1210).

At (S1210), prediction information of a current block is decoded from a coded video bitstream. The prediction information is indicative of a prediction of the current block at least partially based on an inter prediction. In an example, the predication information is indicative of an inter prediction mode, such as a merge mode, a skip mode and the like. In another example, the prediction information is indicative of an intra-inter prediction mode.

At (S1220), a usage of PDPC on the inter prediction is determined based on the prediction information of the current block. In an example, a flag, such as interPDPCflag is received from the coded bitstream and is decoded. In another example, the flag is derived.

At (S1230), samples of the current block are reconstructed. At least a sample of the current block is reconstructed as a combination of a result from the inter prediction and neighboring samples selected based on a position of the sample. In an example, PDPC is applied to the result of inter prediction in a similar manner as the PDPC for intra prediction. Then, the process proceeds to (S1299) and terminates.

It is noted that, in an example, the prediction information is indicative of an intra inter prediction mode that uses a combination of an intra prediction and the inter prediction of the current block, then a motion refinement based on a bi-directional optical flow from the inter prediction of the current block can be excluded. In the example, (S1220) can be skipped, and the decoding is independent of PDPC process.

The techniques described above, can be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media. For example, FIG. 13 shows a computer system (1300) suitable for implementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code or computer language, that may be subject to assembly, compilation, linking, or like mechanisms to create code comprising instructions that can be executed directly, or through interpretation, micro-code execution, and the like, by one or more computer central processing units (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, internet of things devices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the present disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface input devices. Such a human interface input device may be responsive to input by one or more human users through, for example, tactile input (such as: keystrokes, swipes, data glove movements), audio input (such as: voice, clapping), visual input (such as: gestures), olfactory input (not depicted). The human interface devices can also be used to capture certain media not necessarily directly related to conscious input by a human, such as audio (such as: speech, music, ambient sound), images (such as: scanned images, photographic images obtain from a still image camera), video (such as two-dimensional video, three-dimensional video including stereoscopic video).

Input human interface devices may include one or more of (only one of each depicted): keyboard (1301), mouse (1302), trackpad (1303), touch screen (1310), data-glove (not shown), joystick (1305), microphone (1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface output devices. Such human interface output devices may be stimulating the senses of one or more human users through, for example, tactile output, sound, light, and smell/taste. Such human interface output devices may include tactile output devices (for example tactile feedback by the touch-screen (1310), data-glove (not shown), or joystick (1305), but there can also be tactile feedback devices that do not serve as input devices), audio output devices (such as: speakers (1309), headphones (not depicted)), visual output devices (such as screens (1310) to include CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch-screen input capability, each with or without tactile feedback capability—some of which may be capable to output two dimensional visual output or more than three dimensional output through means such as stereographic output; virtual-reality glasses (not depicted), holographic displays and smoke tanks (not depicted)), and printers (not depicted).

Computer system (1300) can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW (1320) with CD/DVD or the like media (1321), thumb-drive (1322), removable hard drive or solid state drive (1323), legacy magnetic media such as tape and floppy disc (not depicted), specialized ROM/ASIC/PLD based devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computer readable media” as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

Computer system (1300) can also include an interface to one or more communication networks. Networks can for example be wireless, wireline, optical. Networks can further be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, and so on. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wireless wide area digital networks to include cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial to include CANBus, and so forth. Certain networks commonly require external network interface adapters that attached to certain general purpose data ports or peripheral buses (1349) (such as, for example USB ports of the computer system (1300)); others are commonly integrated into the core of the computer system (1300) by attachment to a system bus as described below (for example Ethernet interface into a PC computer system or cellular network interface into a smartphone computer system). Using any of these networks, computer system (1300) can communicate with other entities. Such communication can be uni-directional, receive only (for example, broadcast TV), uni-directional send-only (for example CANbus to certain CANbus devices), or bi-directional, for example to other computer systems using local or wide area digital networks. Certain protocols and protocol stacks can be used on each of those networks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storage devices, and network interfaces can be attached to a core (1340) of the computer system (1300).

The core (1340) can include one or more Central Processing Units (CPU) (1341), Graphics Processing Units (GPU) (1342), specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) (1343), hardware accelerators for certain tasks (1344), and so forth. These devices, along with Read-only memory (ROM) (1345), Random-access memory (1346), internal mass storage such as internal non-user accessible hard drives, SSDs, and the like (1347), may be connected through a system bus (1348). In some computer systems, the system bus (1348) can be accessible in the form of one or more physical plugs to enable extensions by additional CPUs, GPU, and the like. The peripheral devices can be attached either directly to the core's system bus (1348), or through a peripheral bus (1349). Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM (1345) or RAM (1346). Transitional data can be also be stored in RAM (1346), whereas permanent data can be stored for example, in the internal mass storage (1347). Fast storage and retrieve to any of the memory devices can be enabled through the use of cache memory, that can be closely associated with one or more CPU (1341), GPU (1342), mass storage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon for performing various computer-implemented operations. The media and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system having architecture (1300), and specifically the core (1340) can provide functionality as a result of processor(s) (including CPUs, GPUs, FPGA, accelerators, and the like) executing software embodied in one or more tangible, computer-readable media. Such computer-readable media can be media associated with user-accessible mass storage as introduced above, as well as certain storage of the core (1340) that are of non-transitory nature, such as core-internal mass storage (1347) or ROM (1345). The software implementing various embodiments of the present disclosure can be stored in such devices and executed by core (1340). A computer-readable medium can include one or more memory devices or chips, according to particular needs. The software can cause the core (1340) and specifically the processors therein (including CPU, GPU, FPGA, and the like) to execute particular processes or particular parts of particular processes described herein, including defining data structures stored in RAM (1346) and modifying such data structures according to the processes defined by the software. In addition or as an alternative, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in a circuit (for example: accelerator (1344)), which can operate in place of or together with software to execute particular processes or particular parts of particular processes described herein. Reference to software can encompass logic, and vice versa, where appropriate. Reference to a computer-readable media can encompass a circuit (such as an integrated circuit (IC)) storing software for execution, a circuit embodying logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration model VVC: versatile video coding BMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplementary Enhancement Information VUI: Video Usability Information GOPs: Groups of Pictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding Tree Units CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: Hypothetical Reference Decoder SNR: Signal Noise Ratio CPUs: Central Processing Units GPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD: Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application-Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within the spirit and scope thereof 

What is claimed is:
 1. A method for video decoding, comprising: receiving prediction information of a current block, the prediction information indicating that a prediction of the current block is at least partially based on an inter prediction; receiving a first flag for an intra-inter prediction mode that uses a combination of an intra prediction and the inter prediction of the current block; determining that a usage of a bi-directional optical flow mode (BDOF) on the inter prediction is applied only when all of the following are satisfied: (1) a height of the current block is not four and a size of the current block is not four by eight, (2) the current block is coded using neither affine mode nor Alternative Temporal Motion Vector Prediction (ATMVP), and (3) a first reference picture used for the inter prediction is prior to the current block in display order and a second reference picture used for the inter prediction is after the current block in display order; and decoding a coded video bitstream based at least on the prediction information indicating the inter prediction and the first flag indicating the intra-inter prediction mode without using the BDOF.
 2. The method of claim 1, wherein the method further comprises: excluding a motion refinement based on the BDOF from the inter prediction of the current block.
 3. The method of claim 1, further comprising: decoding, in response to determining that the first flag indicates true for the intra-inter prediction mode, a second flag that is indicative of a usage of a position dependent prediction combination (PDPC) on the inter prediction; and reconstructing the sample in response to the determination of the usage of the PDPC on the inter prediction.
 4. The method of claim 3, further comprising: decoding, based on a context model for an entropy coding, the second flag that is indicative of the usage of the PDPC.
 5. The method of claim 3, further comprising: applying a filter on neighboring samples of the current block; and reconstructing the sample of the current block as a combination of the result from the inter prediction and the filtered neighboring samples of the current block.
 6. The method of claim 3, further comprising: reconstructing the sample of the current block using neighboring samples of the current block without an application of a filter on the neighboring samples of the current block.
 7. The method of claim 3, further comprising: determining whether the current block meets a block size condition that limits an application of the PDPC in the reconstruction of the current block; and excluding the application of the PDPC in the reconstruction of at least one sample of the current block when the block size condition is met.
 8. The method of claim 7, wherein the block size condition depends on a size of a virtual process data unit.
 9. The method of claim 5, further comprising disregarding a particular neighboring sample in a calculation of the combination when a distance of the particular neighboring sample to the sample is larger than a threshold.
 10. The method of claim 5, further comprising: combining the result from the inter prediction with the neighboring samples that are selected based on a position of the sample and reconstructed based on inter prediction.
 11. The method of claim 3, further comprising: decoding the second flag that is indicative of the usage of the PDPC when the prediction information is indicative of a merge mode.
 12. The method of claim 3, further comprising: decoding, when a flag is indicative of non-zero residue for the current block, the second flag that is indicative of the usage of the PDPC.
 13. An apparatus for video decoding, comprising: processing circuitry configured to: receive prediction information of a current block, the prediction information indicating that a prediction of the current block is at least partially based on an inter prediction; receive a first flag for an intra-inter prediction mode that uses a combination of an intra prediction and the inter prediction of the current block; determine that a usage of a bi-directional optical flow mode (BDOF) on the inter prediction is applied only when all of the following are satisfied: (1) a height of the current block is not four and a size of the current block is not four by eight, (2) the current block is coded using neither affine mode nor Alternative Temporal Motion Vector Prediction (ATMVP), and (3) a first reference picture used for the inter prediction is prior to the current block in display order and a second reference picture used for the inter prediction is after the current block in display order; and decode a coded video bitstream based at least on the prediction information indicating the inter prediction and the first flag indicating the intra-inter prediction mode without using the BDOF.
 14. The apparatus of claim 13, wherein the processing circuitry is further configured to: exclude a motion refinement based on BDOF from the inter prediction of the current block.
 15. The apparatus of claim 13, wherein the processing circuitry is further configured to: decode, in response to determining that the first flag indicates true for the intra-inter prediction mode, a second flag that is indicative of a usage of a position dependent prediction combination (PDPC) on the inter prediction; and reconstruct the sample in response to the determination of the usage of the PDPC on the inter prediction.
 16. The apparatus of claim 15, wherein the processing circuitry is further configured to: decode, based on a context model for an entropy coding, the second flag that is indicative of the usage of the PDPC.
 17. The apparatus of claim 15, wherein the processing circuitry is further configured to apply a filter on neighboring samples of the current block; and reconstruct the sample of the current block as a combination of the result from the inter prediction and the filtered neighboring samples of the current block.
 18. The apparatus of claim 15, wherein the processing circuitry is further configured to reconstruct the sample of the current block using neighboring samples of the current block without an application of a filter on the neighboring samples of the current block.
 19. The apparatus of claim 15, wherein the processing circuitry is further configured to determine whether the current block meets a block size condition that limits an application of the PDPC in the reconstruction of the current block; and exclude the application of the PDPC in the reconstruction of at least one sample of the current block when the block size condition is met.
 20. The apparatus of claim 19, wherein the block size condition depends on a size of a virtual process data unit. 